Cold cathode discharges in argon and argon-nitrogen mixtures were investigated experimentally. Current-voltage characteristics were obtained experimentally for these in microwave sustained discharges. The current-voltage characteristics show current saturating at low values of E/N followed by a rapid increase in current at higher E/N. Lowke's theoretical investigation of gas discharges sustained by an external ionizing source was extended to include microwave excitation. This analysis predicted a similar saturation for the current in the current-voltage characteristics.